Not applicable.
The most commonly constructed residential and municipal water well in the United States is the drilled well because drilling is more cost effective than hand digging and drilled wells can be constructed in a variety of geologic formations. Drilled residential and municipal water well casings are usually sealed on the top and side with the exception of one or more openings that are functionally important such as vents to allow air to flow into and out of the well. When water is pumped from a drilled well, water recharge from the aquifer often occurs at a slower rate than the pumping rate, resulting in a draw down of the water level of the well. Vents allow air to rush into the wells as the water level draws down during the pumping process. Without venting, cavitation can occur in the well during the pumping process and water being pumped from the well becomes turbid. Water well vents are often covered by metal screens to stop insects and other objects from entering into the well. However, these screens do not stop microorganisms from entering into the well.
Bacteria contamination of water wells is a wide spread problem in the United States. A nine-state study has shown that over 34% of the drilled wells tested are coliform positive. Many wells contain hazardous E. coli bacteria. The water well bacteria contamination problem has been dealt with through frequent bacteria testing and disinfecting wells that are tested positive. A common method to disinfect a water well is to treat the well with chlorine. Chlorine has then to be removed through pumping that lasts several hours.
It is an object of the present invention to provide a water well filter device and a method for preventing airborne microorganisms from entering into a water well. The water well filter device of the present invention contains a microorganism filter element having sufficiently small pore sizes to stop microorganisms from passing through. The water well filter device is designed in such a way that when it is mounted to an opening of a water well that is otherwise air-tightly sealed from the open air, the only way that air can enter into the water well is through the microorganism filter element. The water well filter device can further contain a pre-filter, a vacuum relief valve, or both. The pre-filter helps to stop relatively large particles in the air from reaching and clogging the microorganism filter element and thus prolong the usable life of the microorganism filter element. In case that the microorganisms filter element or the pre-filter is clogged up and a negative pressure is built up inside the well during the water pumping process, the vacuum relief valve can open up to allow air enter into the well and thus prevents any undesirable effects caused by the negative pressure inside the well.
In one embodiment, the water well filter device of the present invention is a microorganism filter that contains a microorganism filter element and a housing. The housing has a connection member that allows the microorganism filter to be mounted onto a well opening in an airtight fashion. The filter element is set in the housing in a manner so that the inside of the housing is divided into two compartments and the only way that air can travel inside the housing from one compartment to other is through the filter element. When the filter device is mounted onto a well opening, one compartment of the housing is in gas communication with the open air and the other with the inside of the well. The term xe2x80x9cinside of the wellxe2x80x9d used in the specification and claims refers to the well space on the well side of the microorganism filter element.
The microorganism filter element described above must be able to stop microorganisms such as bacteria and viruses. Different species of bacteria and viruses are different in size. Depending on the specific species of bacterium that needs to be stopped, the filter element can have pores sizes smaller than 100 microns, 10 microns, 5 microns, 2 microns, 1 micron, 0.45 micron, 0.22 micron, or 0.2 micron. Depending on the specific species of virus that needs to be stopped, the filter element can have pore sizes smaller than 0.25 micron, 0.22 micron, 0.1 micron, 0.05 micron, or 0.02 micron. Microorganisms in the air can exist in clusters of multiple microorganisms or other particles. These clusters are larger in size than single microorganisms and can be stopped by a filter element having pore sizes larger than those mentioned above. Accordingly, a filter element having pore sizes larger than those mentioned above can also be used in the present invention. Any suitable filter medium that has pore sizes sufficiently small to stop bacteria or viruses can be used as the filter element. For example, a conventional paper filter, polypropylene membranes from Osmonics (Kent, Wash.), or Teflon PTFE membranes from Osmonics can be used. The filter housing can be made of durable materials such as metal or hard plastic.
The microorganism filter element is susceptible to being clogged up due to its small pore sizes. To prolong the useable life of the microorganism filter element, another embodiment of the filter device of the present invention further contains a pre-filter with a pre-filter element for filtering out relatively large particles such as dust particles, leave debris and insects from the air before it reaches the microorganism filter element. Depending on the size of the particles that need to be pre-filtered, the pre-filter element can be a metal screen, a screen made of other materials, or a filter element with pore sizes larger than those of the microorganism filter element. In the filter device, the pre-filter is positioned ahead of the microorganism filter element in the airflow pathway from the open air to the inside of the water well so that almost all of the air flowing into the well, if not all, has to pass through the pre-filter element before reaching the microorganism filter element. Preferably, the pre-filter contains a connection member allowing it to be assembled into and disassembled from the filter device easily. As a result, the pre-filter can be replaced without replacing the microorganism filter element.
When either or both of the microorganism filter element and the pre-filer element are clogged up so that air can not enter into the water well, a negative pressure can build up inside the well while water is being pumped out. This may lead to the suction of the water that accumulated around the water well casing above ground water level into the well and further being pumped out. Such water may be contaminated by microorganisms and toxics in the soil and thus pose a risk to human health. To reduce this risk, another embodiment of the filter device of the present invention further contains a vacuum relief valve. The valve has a connection member that allows the valve to be connected to the inside of the well in an airtight fashion. The valve open ups at a preset pressure level allowing outside air to enter into the well. Optionally, the valve contains a whistle for alerting people to check and change either or both of the microorganism filter and the pre-filter. Also optionally, the valve is connected to a valve filter in a fashion so that when the valve opens up, the only way that air can enter into the inside of the well is to go through the valve filter. The valve filter has a filter element that stops certain particles in the air from entering into the well when the valve opens up. The pore sizes of the valve filter element depend the size of the particles that need to be stopped. For example, the valve filter element can be similar to the pre-filter element or the microorganism filter element described above.
The device of the present invention can be used for both residential or municipal wells. The municipal wells are bigger than residential wells and thus the filter device for municipal wells, including the microorganism filter, the pre-filter and the vacuum relief valve is usually larger than that for residential wells.
In still another embodiment, the present invention is a method for preventing airborne microorganisms from entering into a residential or municipal water well. The method involves mounting the water well filter device of the present invention described above to an opening of a water well that is otherwise sealed from the open air. When the filter device mounted does not contain a vacuum relief valve and it is desirable to provide a vacuum relief mechanism, the method of the present invention further involves independently connecting a vacuum relief valve to the inside of the well. Optionally, a valve filter is deployed as well.
Other objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of specific embodiments taken in conjunction with the accompanying drawings.